Now execute “sfill /tmp/&” where /tmp/ is the folder name. It may take hours to run through multiple fill-delete cycles.

However, to be 100% sure that no data can be ever restored you will need to delete the partition(s), create a new partition and format this partition with your new filesystem of your choice. Then install Linux OS, secure-delete tool and run it in “paranoid” mode for hours, perhaps days depending on how large is the partition and how fast is the filesystem.